In the early part of the twentieth century, the American naturalist William Beebe came upon a strange sight in the Guyana jungle. A group of army ants was moving in a huge circle. The circle was 1,200 feet in circumference, and it took each ant two and half hours to complete the loop. The ants went around and around the circle for two days until most of them dropped dead.

What Beebe saw was what biologists call a “circular mill.” The mill is created when army ants find themselves separated from their colony. Once they’re lost, they obey a simple rule: follow the ant in front of you. The result is the mill, which usually only breaks up when a few ants straggle off by chance and the others follow them away.

As Steven Johnson showed in his illuminating book Emergence, an ant colony normally works remarkably well. No one ant runs the colony. No one issues orders. Each individual ant knows, on its own, almost nothing. Yet the colony successfully finds food, gets all its work done, and reproduces itself. But the simple tools that make ants so successful are also responsible for the demise of the ants who get trapped in the circular mill. Every move an ant makes depends on what its fellow ants do, and an ant cannot act independently, which would help break the march to death.

So far in this book, I’ve assumed that human beings are not ants. In other words, I’ve assumed that human beings can be independent decision makers. Independence doesn’t mean isolation, but it does mean relative freedom from the influence of others. If we are independent, our opinions are, in some sense, our own. We will not march to death in a circle just because the ants in front of us are.

This is important because a group of people—unlike a colony of ants—is far more likely to come up with a good decision if the people in the group are independent of each other. Independence is always a relative term, but the story of Francis Galton and the ox illustrates the point. Each fairgoer figured out his estimate of the weight of the ox on his own (with allowances made for kibitzing), relying on what economists call ‘private information.” (Private information isn’t just concrete data. It can also include interpretation, analysis, or even intuition.) And when you put all those independent estimates together, the combined guess was, as we’ve seen, near perfect.

Independence is important to intelligent decision making for two reasons, First, it keep the mistakes that people make from becoming correlated. Errors in individual judgment won’t wreck the group’s collective judgment as long as those errors aren’t systematically pointing in the same direction. One of the quickest ways to make people’s judgments systematically biased is to make them dependent on each other for information. Second, independent individuals are more likely to have new information rather than the same old data everyone is already familiar with. The smartest groups, then, are made up of people with diverse perspectives who are able to stay independent of each other. Independence doesn’t imply rationality or impartiality, though. You can be biased and irrational, but as long you’re independent, you won’t make the group any dumber.

Now, the assumption of independence is a familiar one. It’s intuitively appealing, since it takes the autonomy of the individual for granted. It’s at the core of Western liberalism. And, in the form of what’s usually called “methodological individualism,” it under- pins most of textbook economics. Economists usually take it as a given that people are self-interested. And they assume people arrive at their idea of self-interest on their own.

For all this, though, independence is hard to come by. We are autonomous beings, hut we are also social beings. We want to learn from each other, and learning is a social process. The neighborhoods where we live, the schools we attend, and the corporations where we work shape the ay we think and feel. As Herbert J. Simon once wrote, “A man does not live for months or years in a particular position in an organization, exposed to some streams of communication, shielded from others, without the most profound effects upon what he knows, believes, attends to, hopes, wishes, emphasizes, fears, and proposes.”

Even while recognizing (how could they not?) the social nature of existence, economists tend to emphasize people’s autonomy and to downplay the influence of others on our preferences and judgments. Sociologists and social-network theorists, by contrast, describe people as embedded in particular social contexts, and see influence as inescapable. Sociologists generally don’t view this as a problem. They suggest it’s simply the way human life is organized. And it may not be a problem for everyday life. But what I want to argue here is that the more influence a group’s members exert on each other; and the more personal contact they have with each other, the less likely it is that the group’s decisions will be wise ones. The more influence we exert on each other, the more likely it is that we will believe the same things and make the same mistakes. That means it’s possible that we could become individually smarter but collectively dumber. The question we have to ask in thinking about collective wisdom, then, is: Can people make collectively intelligent decisions even when they are in constant, if erratic, interaction with each other?